1. Field of the Invention
The present invention relates to an optical transmission device. More particularly, it relates to a plugjack type optical/electric transmission device for transmitting and receiving optical and electric signals.
2. Description of Related Art
As shown in FIG. 8, Japanese Unexamined Patent Publication No. 2000-347074 discloses a photoelectric conversion module utilized in an optical/electric transmission device.
Referring to FIG. 8, a photoelectric conversion module 100 includes a casing 101, a light receiving element 103, a light emitting element 104, an electric circuit board 107 on which an electric driving circuit for transmission and an electric circuit for reception are mounted, and connector pins 108 for electrically connecting the electric circuits mounted on the electric circuit board 107 with external electric circuits.
Further, the photoelectric conversion module 100 includes a ferrule holder 105 having a receiving ferrule holder 105b and a transmitting ferrule holder 105c which are integrally formed. The receiving ferrule holder 105b functions to hold a transmitting ferrule holder of an optical plug inserted through optical plug jacks 101b and 101c in a predetermined position for optical connection with a light emitting element assembly. The transmitting ferrule holder 105c functions to hold a receiving ferrule holder of the optical plug inserted through the optical plug jacks 101b and 101c in a predetermined position for optical connection with a light receiving element assembly.
FIG. 9 is a plan view illustrating a conventional optical/electric transmission device module manufactured under the standards of ATM and IEEE 1394.b and FIG. 10 is a front view of the same.
Referring to FIGS. 9 and 10, a module 200 includes a holder 202 for detachably holding an optical plug 201. In the holder 202, a transmitting connector and a receiving connector are formed integrally and a light emitting element 203 and a light receiving element 204 are mold-packaged.
The holder 202 is placed on a circuit board 207 on which an integral circuit section 205 for driving the light emitting element and an amplifying integral circuit section 206 for the light receiving element are mounted. Further, the holder 202 has connection terminals 208 for electrically connecting the electric circuits mounted on the circuit board 207 with external electric circuits.
Japanese Unexamined Patent Publication No. Hei 11 (1999)-345987 describes a method of mounting a transmitting/receiving module for optical linkage which is comprised of an opening through which an optical fiber is inserted, a light receiving element and a light emitting element which carry the inserted optical fiber and first, second and third substrates connected to the elements.
According to the above-described conventional photoelectric conversion modules 100 (FIG. 8) and 200 (FIG. 9), the driving circuits are arranged at the back of the light receiving element and the light emitting element.
Therefore, the amount of wasted space grows above the circuit board 107 in the module 100 or above the integral circuit sections 205 and 206 in the module 200. As a result, the housing or the circuit section substantially occupies quite a large space in the device.
On the other hand, if the electric driving circuit for the light emitting element and the electric circuit for the light receiving element are formed integrally, electromagnetic coupling noise tends to be caused from the light emitting element and the driving circuit thereof to the light receiving element and the electric circuit thereof and vice versa.
According to the transmitting/receiving module for optical linkage disclosed in Japanese Unexamined Patent Publication No. Hei 11 (1999)-345987, a substrate connection terminal extends backward from the rear side of the light receiving element and the light emitting element, i.e., in a direction opposite to the opening with reference to the light receiving element and the light emitting element. Further, a transmitting/receiving electric circuit board is arranged further backward via the substrate connection terminal. Therefore, the module has quite a large length along the insert direction of the optical fiber.